Today’s poll puts Yes on 38%, up four points on a month ago. No are on 47%, also up on last month but by a more modest two points. Don’t Knows (which have tended to be relatively high in ICM’s polls) have fallen by no less than seven points from 21% to 14%, suggesting that undecided voters have indeed begun to make up their mind as polling day approaches.

Once the Don’t Knows are excluded the Yes tally stands at 45%, No at 55%, representing a two point swing from No to Yes since last month. A movement of that size is too small for us to be able to rule out the possibility that it has simply occurred by chance, and in any event it simply puts the Yes vote back to where it was in ICM’s poll in June. Today’s poll is thus best regarded as failing to show that No has gained any longer-term advantage from the leaders’ debate than as evidence of a renewed swing to Yes.

As well as fewer voters saying they are undecided, the poll also reveals an increased commitment to vote. As many as 71% now say they are certain to vote, up from 65% in ICM’s previous poll and the highest figure to be recorded by the company since it first started tracking propensity to vote in May. In line with many a previous poll, Yes voters are rather more committed to voting than No voters; indeed, taking into account voters’ reported propensity to vote (as ICM have done) adds two points to its estimate of the Yes vote, which otherwise would stand at 43% (after Don’t Knows are excluded).

Nevertheless, but for the relief that the Yes side probably feels at perhaps not having lost ground in the last fortnight after all (our poll of polls remains at Yes 43%, No 57%), there is still plenty in this poll that should concern it.

First, the leaders’ debate was meant to be an opportunity for it to advance its cause. However 42% of (all) voters reckon that Mr Darling won, while only 19% feel that Mr Salmond did. Even amongst Yes supporters, only 46% think that Mr Salmond was the winner. The opportunity was clearly missed.

Second, the Yes side’s hopes of narrowing the gap in the final weeks of the campaign appeared to rest heavily on winning over undecided voters. Yet even though there are now fewer of them, there has not been a significant increase in Yes support. Moreover, those voters who remain undecided do not appear particular likely eventually to vote Yes. When asked which way they think they will vote, those (some two in five) who give an answer break two to one in favour of No. When the undecided are invited to declare their stance on independence on the scale from one to ten that the Yes side has been using in its canvassing, 75% of those who give an answer (and three in four do) give themselves a score of five or less, indicating that they are more inclined to be opposed to than supportive of independence.

Third, although the No side’s promises of more devolution are still not widely believed – still no more than 41% think that more devolution would actually be delivered – few No voters who want more devolution say they would switch sides if they were to be convinced it would not happen. No less than 85% of them say they will vote No anyway, while just 9% say they would vote Yes. Repeating the claim that more devolution will not happen seems unlikely to bring the Yes side much reward.

Finally, and perhaps most importantly, the Yes side continue to make little or no progress on convincing voters on the central issue in the campaign – whether or not independence would be good or bad for Scotland’s economy. Just 34% say that Scotland’s economy would be better under independence, while 45% believe it would be worse. The difference between these two figures has changed little during the course of the summer.

However, there is also some less than comfortable reading for the No side in this poll. For all its self-confidence that the currency issue is finally proving to be a winner, today’s poll echoes the findings of last week’s Survation’s poll in suggesting that the claim that an independent Scotland would not be able to keep the pound in a monetary union with the rest of the UK is no more widely believed now than it was back in February, when the announcement was originally made. As many as 45% still think that a monetary union would be created in the wake of a Yes vote, down just two points on six months ago. Only 38% believe this would not happen, up just three. No less than 80% of Yes voters disbelieve the claim, which doubtless helps explain why they are still willing to vote Yes even though two-thirds of them would like to keep the pound.

Not that the Yes side can afford to be complacent about the currency issue. If the claims of the No side are treated with scepticism, there are widespread doubts about the credibility of the Scottish Government’s plans on currency too. Just 26% believe that they are ‘convincing’ while 52% consider them ‘unconvincing’. Mr Salmond may not want to tell us what his Plan B is, but he does need to convince us that he does indeed have some kind of realistic plan.